Comparison of Three Methods for Determining Young's Modulus of Wood
摘要
Values of Young's modulus of China fir, Taiwan red cypress, Taiwan yellow cypress, Japanese cedar, and camphor wood were investigated in this study. These wood species are most typical of the wood used in historic buildings in Taiwan. Discussions of apparent and true Young's moduli obtained from longitudinal-and complex-vibration tests and a comparison of these results with tests of the same specimens by the static-bending method are presented. A simultaneous determination of the shear modulus (G) of test specimen was obtained by a complex-vibration bending and twisting method. Results showed that the longitudinal-vibration method yielded the highest values for the apparent Young's modulus, and those from the static-bending method were the lowest. Values of the percentage differences between values of Young's modulus obtained from different test methods increased with an increase in E(subscript b)/G values. Based on the Timoshenko beam theory and Hearmon approximate solution method, taking rotary inertia and shear deformation into account, it was observed that a very high correlation (R^2 = 0.999) existed between the true Young's modulus obtained from the complex-vibration and static-bending tests. There was a tendency for the dy-namic measurements to be approximately 1.2% on average higher than the static measurements. The accuracies of the apparent Young's modulus obtained from both the complex-vibration and static-bending tests improved as the E-to-G ratios decreased, and this parameter could be used as a guideline for the expected accuracy of the apparent Young's modulus corresponding to various test methods.